Modified skin cells that may help protect cultured skin substitutes from infection

Cincinnati burn researchers have created genetically modified skin cells that, when added to cultured skin substitutes, may help fight off potentially lethal infections in patients with severe burns.

Dorothy Supp, PhD, and her team found that skin cells that were genetically altered to produce higher levels of a protein known as human beta defensin 4 (HBD4) killed more bacteria than normal skin cells.

HBD4 is one in a class of proteins that exist throughout the body as part of its natural defense system. Researchers have only recently begun targeting these tiny molecules as a way to combat infections.

"If we can add these genetically modified cells to bioengineered skin substitutes, it would provide an important defense system boost during the initial grafting period, when the skin is most susceptible to infection," explains Supp, an adjunct research associate professor at the University of Cincinnati (UC) and researcher at Cincinnati Shriners Hospital for Children.

Supp says defensins could become an effective alternative method for burn wound care and infection control. Using them in cultured skin substitutes, she adds, could also decrease a patient's risk for infection, improve skin graft survival and reduce dependence on topical antibiotics.

UC researchers report these findings in the January issue of the Journal of Burn Care and Research.

Cultured skin substitutes are grown in a laboratory using cells from a burn patient's own skin. These cells are cultured, expanded and combined with a spongy layer of collagen to make skin grafts that are reattached to the burn wound.

"Cultured skin substitutes are improving the lives of many burn patients, but they also have limitations--including an increased susceptibility to infection," says Supp. "Because cultured skin grafts aren't connected to the circulatory system at the time of grafting, they aren't immediately exposed to circulating antibiotic drugs or antibodies from the body's immune system to fight off infection."

Currently, physicians manage cultured skin graft infections during the early healing period by continually wrapping the wound in dressings soaked in antimicrobial drugs. Although this protects the grafts, Supp says, it can also contribute to the emergence of drug-resistant strains of bacteria.

"When you give the patient the same drug topically and orally, the risk for drug-resistant bacteria to emerge is greatly increased," says Supp. "We need alternative methods for combating infection in burn patients.

In this three-year laboratory study, Supp isolated the HBD4 gene from donated tissue samples and transferred it into surface skin cells (keratinocytes) to give them enhanced infection-fighting abilities. These cells were then infected with pseudomonas aeruginosa, a type of bacteria found commonly in hospitals, and allowed to incubate. Analysis revealed that the genetically altered cells containing HBD4 were more resistant to microbial infections than the unaltered cells.

"If it proves effective in additional testing," Supp predicts, "this type of gene therapy could be a promising alternative infection control method for burn wounds."

Researchers hope to begin testing this approach in an animal model in early 2007.